Aspergillus fumigatus, a ubiquitous fungus, causes substantial morbidity and mortality in humans, principally those with compromised immunity by genetic predisposition or iatrogenic immunosuppression. Although primarily a respiratory tract pathogen, via inhalation of airborn spores, little is known about the precise events and interactions with the host that lead to successful survival and propagation of the fungus. We have cloned a gene controlling the hydrophobicity of A. fumigatus conidia in order to study its role in the survival and growth of the fungus in the host tissue. Polymerase chain reaction (PCR) method was used to clone a hydrophobin which has been identified in other nonpathogenic fungi. The sequence of a 400 bp DNA fragment, generated by PCR from A. fumigatus DNA, showed 80.6% similarity to a hydrophobin gene (ROD A) of A.nidulans. A lambda genomic DNA library was screened with the 400 bp fragment and the genomic subclone containing this 400 bp DNA was sequenced. The amino acid sequence showed 8 cysteines arranged in a pattern similar to that observed in the ROD A protein of the conidial wall in A.nidulans and to three cell wall proteins of a mushroom species, Schizophillum commune.